Moulds

ABSTRACT

A reinforced mould, including a mould body having a mould cavity in at least one end surface thereof, the mould body has arranged along at least part of its axial length a pre-tensioned reinforcing means in the form of at least one winding of thin metallic strip material, wherein the width of the wound turns of reinforcing winding, as seen in axial section, decreases radially outwardly from the periphery of the mould body to provide a pretensioning force which varies along the mould body proportionally to the forces exerted therein when the mould is used.

United States Patent Strandell [451 Sept. 19,1972

[ MOULDS 3,461,506 8/1969 Rice et al. ..l8/34 R [72] Inventor: gag-013iSjtrandell, Bockstigen 3, Primary Examiner Mnton S Mehr a we enAttorney-Stevens, Davis, Miller& Mosher [22] Filed: June 19, 1970 [21]Appl. No.: 47,683

[30] Foreign Application Priority Data June 25, 1969 Sweden ..9024/69521 US. Cl ..72/467 511 int. Cl ..B2lc 3/00 [58] Field of Search....72/467; 18/34 R; 29/446, 452;

[57] ABSTRACT A reinforced mould, including a mould body having aprovide a pre-tensioning force which varies along the 76/107; 52/224mould body proportionally to the forces exerted I therein when the mouldis used. [56] References Cited 3 Claims, 3 Drawing Figures UNITED STATESPATENTS 3,550,213 12/1970 Ormsby et a] ..18/34 R /5/ t l i I l E l M i lj 5 MOULDS The present invention relates to a mould of the type whichincludes a mould body having a mould cavity in at least one end surfacethereof and being encircled along at least part of its axial length by apretensioned reinforcement comprising at least one winding of metallic,strip material which has a thickness of at most of a few tenths of amillimeter, and the whole of the bottom face of each turn of a windingbeing in abutment with the upper face of the preceding turn of saidwinding.

When producing articles by forging or by powder compacting processes inmoulds of the aforementioned type, more fully described in my U.S. Pat.No. 3,608,351 issued Sept. 28, 1971, the stresses appearing in themoulds normally vary greatly along the length of the mould body. Thus,when using a mould having a cup shaped, blind mould cavity thetangential tension forces appear in relation to the diameter or width ofthe cavity, so that the forces acting at the bottom of the cavity have asmall magnitude when compared with the tangential tension forcesoccuring at locations remote from the bottom. This can give rise totroublesome shear forces in the mould body adjacent the bottom of thecavity, especially in the case of moulds subjected to heavy loads. Whenusing moulds of the type which have a cavity passing axially through itin which, for example, metal powder or the like is compacted by means oftwo pistons forced in to the mould cavity from their respective ends ofthe mould body, the tangential tensile forces increase from zero at theends of the body to maximum at a region remote from the ends. Because ofthis the mould cavity is likely to be widened at the region subjected tothe maximum forces, thus rendering it difficult to eject the compactedpowdered articles and possibly resulting in damage thereto.

These disadvantages can to a certain extent be eliminated by employingseveral windings and using windings having more turns and/or affording ahigher degree of pre-tension in regions of the mould body which aresubjected to higher stresses than other regions thereof, as described insaid U.S. Pat. No. 3,608,351, although the occurrence of abruptvariations in pretensioning forces at certain regions along the body cannever by avoided by means of these arrangements and hence in certaincases the mentioned inconveniences still remain to a troublesome degree.

In order to remove these inconveniences more fully it is suggested inaccordance with the invention that with a mould of the type describedabove, the width of the winding or the width of at least some of thewindings when viewed in axial section is made to decrease radiallyoutwards from the periphery of the body in a manner whereby thepre-tensioning force applied to the body through the winding or windingsvaries along the length of the body, substantially in proportion to theradial and peripheral forces acting thereon when the mould is beingused.

A mould according to the invention can of course be produced by wrappingaround the body at least one strip or band whose width progressivelydecreases in accordance with a specific pattern, whereby the desiredvariation in pre-tensioning is obtained along the length of the mouldbody. This method of obtaining the variation in pre-tension is, however,both impractical and expensive. A simpler and more economic methoddespite a certain loss of material is to reinforce the mould inaccordance with the invention, by mechanically machining the winding orat least some of the windings, e.g. on a lathe or by grinding, in amanner whereby the width of the winding, when viewed in axial section,decreases radially outwards from the periphery of the mould body and thepre-tensioning forces applied to the body by the winding or windings arecaused to vary along the length of the body, substantiallyproportionally to the forces created thereon when the mould is beingused.

The invention will now be described with reference to a number ofembodiments shown diagrammatically in the accompanying drawing, inwhich:

FIG. 1 is an axial sectional view of a first mould constructed accordingto the invention; and,

FIGS. 2 and 3 illustrate in axial section a second and a third mouldaccording to the invention.

FIG. 1 illustrates diagrammatically a mould body 10 having at its oneend surface 11 a blind mould cavity 12. Extending axially through thebody 10 from the bottom of the cavity is a bore 13 adapted to accomodatean ejector pin. Arranged around the body 10 is a reinforcement in theform of a winding 14 of thin, metallic strip material, the thickness ofwhich should preferably not exceed 0.4 mm and is preferably less than0.2 mm. The thickness of the strip is preferably only few hundreths of amillimeter as described in said U.S. Pat. No. 3,608,351. Holes and otherarrangements located on the mould to facilitate its positioning in amoulding apparatus, such as a foundry press, have been omitted for thesake of clarity. The external configuration of the mould body 10 may becylindrical or, when considered suitably, may have a cross sectionalshape which is other than circular. For example, when the mould cavityhas an elongated shape in cross section it said comers, the bodyportions being held together solely by means of the winding 14. Thewinding 14 can be formed to advantage with strip material of uniformwidth along the whole of its length, the winding thereby obtaining thecontours shown by broken lines 15. The winding can then be machinedmechanically, on a lathe or by grinding for example, so that seen inaxial section the radial thickness varies along the length of the mouldbody in the desired manner.

In FIGS. 2 and 3 the mould body, here identified by the referencenumeral 16, has a cavity 17 passing the mould being mould cavity 17 andencircled by a reinforcement consisting of a thin, metallic stripmaterial. The mould is intended for use in compacting powdered material.When compacting the material, two pistons are forced into the cavity 17in a conventional manner from their respective ends 18 and 19 of themould body 16. The pistons and the means for ejecting the compactedpowder bodies have not been shown, since they form no part of theinvention.

The profile given to the reinforcements shown in FIGS. 2 and 3 is alsosuch that the pre-tensioning forces applied to the body 16 vary alongthe length of said body essentially proportionally to the forcesoccuring on the body, when the tool is being used. The embodimentillustrated in FIG. 2 comprises two windings 20 and 21 which, asindicated by the dash lines 22 and 23, have been made by using wider andnarrower metal strips, which have uniform width along their lengths, andthen machined in accordance with the invention to obtain the desiredvariation in thickness. The reinforcement shown in FIG. 3 comprises athin metal strip winding 24. in addition to the winding 24 the mouldbody 16 in this exemplary embodiment has also been machined in a mannerwhereby the ends 18 and 19 of the mould body present charnfered surfaces25 which are in contact withsupport rings 26 which protect the winding24on the mould body and whichare adapted to be fixed in a mould holder ina known manner.

The invention is not restricted to the described and illustratedembodiments, but can be varied within the scope of the following claims.

What is claimed is:

1. A mould of the type including a mould body having a mould cavity inat least one end surface thereof and being encircled along at least partof its axial length by a pre-tensioned reinforcement comprising at leastone winding of metallic, strip material which has a thickness of at most0.5 millimeters with the whole of the bottom face of each turn of awinding being in abutment with the upper face of the preceding turn ofsaid winding, and when viewed in axial section the width of windingsdecreasing radially outwards from the periphery of the mould body in amanner whereby the pre-tensioning force applied to the body through thewindings varies along the length of the mould body essentially inproportion to the radial and peripheral forces occuring on the body whenthe mould is being used.

2. A mould according to claim 1, including protecting support ringsabout the winding, each ring abutting a respective end of the mouldbody.

3. A mould according to claim 1, wherein the thickness of the stripmaterial is less than 0.2 mm.

1. A mould of the type including a mould body having a mould cavity inat least one end surface thereof and being encircled along at least partof its axial length by a pre-tensioned reinforcement comprising at leastone winding of metallic, strip material which has a thickness of at most0.5 millimeters with the whole of the bottom face of each turn of awinding being in abutment with the upper face of the preceding turn ofsaid winding, and when viewed in axial section the width of windingsdecreasing radially outwards from the periphery of the mould body in amanner whereby the pre-tensioning force applied to the body through thewindings varies along the length of the mould body essentially inproportion to the radial and peripheral forces occuring on the body whenthe mould is being used.
 2. A mould according to claim 1, includingprotecting support rings about the winding, each ring abutting arespective end of the mould body.
 3. A mould according to claim 1,wherein the thickness of the strip material is less than 0.2 mm.